Impact of Hypercapneic Hyperventilation and the ANEclear Device on Recovery of
Pharyngeal Function After Sevoflurane Anesthesia

R. McKay1, K. T. Hall2
Anesthesia and Perioperative Care, University of California San Francisco, San Francisco, CA, 2University of California San Francisco, San Francisco, CA.

Introduction: Previous investigation has shown faster emergence after sevoflurane when the ANEclear device is used in conjunction with hypercapneic hyperventilation (1). ANEclear contains a filter that removes volatile anesthetic and increases dead space in the circuit, allowing hyperventilation without concomitant decrease in PaC02. Whether this faster emergence correlates with faster elimination of small MAC-fractions of anesthetic and recovery of normal pharyngeal function is unknown. Sub-hypnotic MAC-fractions of sevoflurane have been shown to impair pharyngeal function in healthy volunteers (2) and patients (3).

Methods:
Forty-four patients undergoing laparoscopic surgery were randomly assigned to standard versus ANEclear emergence. All received 2 mg midazolam, fentanyl 1 µg/kg, propofol 2 mg/kg, and succinylcholine 1 mg/kg. Anesthesia was maintained with sevoflurane at end-tidal 1.7-2.0% in oxygen, fentanyl 1.5 µg/kg/hour, and rocuronium 0.3 mg/kg/hour, titrated to acceptable surgical relaxation. End-tidal CO2 was maintained between 35-38mmHg. All received ondansetron 4 mg and 70 µg/kg neostigmine + 10-14 µg/kg glycopyrrolate prior to extubation.

At the conclusion of surgery, sevoflurane was discontinued and oxygen flow increased to 10 L/min. In the device group, minute ventilation was doubled and end-tidal CO2 targeted at 50-60 mmHg. Control group was ventilated to end-tidal CO2 between 38-45 mmHg. A blinded observer noted time from discontinuation of sevoflurane until first response to command, and, at pre-determined intervals thereafter (2,6,14,22 and 30 minutes), ability to swallow 20 mL of water according to a protocol described previously (3). Secondary outcomes (100-mmVAS for nausea, pain, energy and wakefulness) were measured at 15-minute intervals during the first hour and at 24 hours after emergence.

Statistical analysis was by Mann-Whitney, chi square or t-test where appropriate.

Results:
Patients receiving the device had longer anesthetic and greater MAChours, although these differences were not statistically significant (table). Device subjects received more fentanyl and rocuronium, although amounts were similar when considered as a function of anesthetic duration.

Time from discontinuation of sevoflurane until first response to command and ability to swallow were shorter in patients receiving the device (table). There was a non-significant trend toward greater ability to swallow at 2 and 6 minutes after response to command .

Antiemetic rescue was more prevalent, and nausea more frequent and severe, at 15 and 30 minutes after emergence in the control group. Other secondary outcomes (pain, wakefulness and energy) were similar between groups.

Discussion:
These findings confirm that pharyngeal recovery after sevoflurane is faster with hypercapneic hyperventilation+ANEclear compared to standard management. These findings may have been minimized by greater sevoflurane MAChours, a factor known to correlate with delayed pharyngeal recovery (4). Impact on early nausea may reflect more efficient elimination of small MAC fractions of sevoflurane.

References:
1. Anesth Analg 2007;105:79-82.
2. Anesthesiology 2001;95:1125-32.
3. Anesth Analg 2005;100:697-700.
4. Anesthesiology 2008;A1203.

Demographic Data & Results
Number of subjects Treatment (ANEclear)
22
Control
22
P-Value
Age (years)
Gender (% female)
ASA I/II/II
22
64
8/12/2
22
77
9/9/4
N.S.
N.S.
N.S.
Minutes sevoflurane
MAC hours sevoflurane
BMI (kg/m2)
196 ± 64
3.28 ± 1.11
26.5 ± 5.5
166 ± 49
2.81 ± 0.85
27.5 ± 5.7
0.09
0.12
N.S.
Fentanyl µ/k (µ/k/h)
Rocuronium µ/k (µ/k/h)
6.81±2.59 (2.16±0.55)
0.82±0.27 (0.28±0.12)
5.19±1.37 (1.98±0.59)
0.56±0.20 (0.22±0.10)
0.013 (0.28)
0.001 (0.14)
Response to command after discontinuation of sevoflurane (seconds) 350 ± 133 569 ± 342 0.027
Time first able to swallow after discontinuation of sevoflurane (seconds) 655 ± 305 1081 ± 571 0.045
Nausea (VAS 0-10)
15 minutes
30 minutes
0.00 ± 0.00
0.18 ± 0.66
2.34 ± 2.66
1.39 ± 2.49
0.0002
0.0456
45 minutes
60 minutes
24 hours
0.95 ± 2.10
0.73 ± 1.78
1.22 ± 2.25
1.40 ± 2.09
1.39 ± 1.99
2.59 ± 4.17
N.S.
N.S.
N.S.
Rescue antiemetic, PACU
0-30 minutes, n (%)
0-60 minutes, n (%)
1 (4.5)
2 (9.0)
7 (32)
8 (36)
0.019
0.031
Opioid in PACU,
0-30 minutes
n (%)
22 (100) 19 (86) N.S.
 

 

 

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